1. Field of the Invention
The present invention relates to silicon carbide layers and, more particularly to a method of forming silicon carbide layers.
2. Background of the Invention
Integrated circuits have evolved into complex devices that can include millions of components (e.g., transistors, capacitors and resistors) on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit densities. The demands for greater circuit densities necessitates a reduction in the dimensions of the integrated circuit components.
As the dimensions of the integrated circuit components are reduced (e.g., sub-micron dimensions), the materials used to fabricate such components contribute to the electrical performance of such components. For example, low resistivity metal interconnects (e.g., aluminum and copper) provide conductive paths between the components on integrated circuits.
Typically, the metal interconnects are electrically isolated from each other by a bulk insulating material. When the distance between adjacent metal interconnects and/or the thickness of the bulk insulating material has submicron dimensions, capacitive coupling potentially occurs between such interconnects. Capacitive coupling between adjacent metal interconnects may cause cross-talk and/or resistance-capacitance (RC) delay, which degrades the overall performance of the integrated circuit.
In order to minimize capacitive coupling between adjacent metal interconnects, low dielectric constant bulk insulating materials (e.g., dielectric constants less than about 3.0) are needed. Typically, bulk insulating materials with dielectric constants less than about 3.0 are tensile materials (e.g., tensile stresses greater than about 108 dynes/cm2). Examples of low dielectric constant bulk insulating materials include silicon dioxide (SiO2), silicate glass, and fluorosilicate glass (FSG), among others.
In addition, a low dielectric constant (low k) barrier layer often separates the metal interconnects from the bulk insulating materials. The barrier layer minimizes the diffusion of the metal from the interconnects into the bulk insulating material. Diffusion of the metal from the interconnects into the bulk insulating material is undesirable because such diffusion can affect the electrical performance of the integrated circuit (e.g., cross-talk and/or RC delay); or render it inoperative.
Some integrated circuit components include multilevel interconnect structures (e.g., dual damascene structures). Multilevel interconnect structures can have two or more insulating layers, low dielectric barrier layers, and metal layers stacked one on top of another. When bulk insulating materials that are tensile are incorporated into a multilevel interconnect structure, such interconnect structure can undesirably crack and/or peel away from an underlying substrate.
The demands for greater integrated circuit densities also impose demands on the process sequences used for integrated circuit manufacture. For example, in process sequences using conventional lithographic techniques, a layer of energy sensitive resist is typically formed over a stack of material layers on a substrate. Many of these underlying material layers are reflective to ultraviolet light. These reflections can distort the dimensions of features such as lines and vias that are formed in the energy sensitive resist material.
One technique proposed to minimize reflections from an underlying material layer utilizes an anti-reflective coating (ARC). The ARC is formed over the reflective material layer prior to resist patterning. The ARC suppresses the reflections off the underlying material layer during resist imaging, providing accurate pattern replication in the layer of energy sensitive resist.
Silicon carbide (SiC) has been suggested for use as a barrier layer and/or ARC on integrated circuits, since silicon carbide layers can have a low dielectric constant (dielectric constant less than about 5.5), are good metal diffusion barriers and can have good light absorption properties.
Therefore, there is an ongoing need for a method of forming silicon carbide films with low dielectric constants and improved film characteristics that are also suitable for use as ARCs.
A method of forming a silicon carbide layer for use in integrated circuit fabrication processes is provided. The silicon carbide layer is formed by reacting a gas mixture comprising a silicon source, a carbon source, and a nitrogen source in the presence of an electric field. The as-deposited silicon carbide layer incorporates nitrogen therein from the nitrogen source.
The silicon carbide layer is compatible with integrated circuit fabrication processes. In one integrated circuit fabrication process, the silicon carbide layer is used as both a hard mask and a barrier layer for fabricating integrated circuit structures such as, for example, a dual damascene structure. For such an embodiment, a preferred process sequence includes depositing a silicon carbide barrier layer on a metal layer formed on a substrate. After the silicon carbide barrier layer is deposited on the substrate a first dielectric layer is formed thereon. A silicon carbide hard mask layer is formed on the first dielectric layer. The silicon carbide hard mask is patterned to define vias therein. Thereafter, a second dielectric layer is formed on the patterned silicon carbide hard mask layer. The second dielectric layer is patterned to define interconnects therein. The interconnects formed in the second dielectric layer are positioned over the vias defined in the silicon carbide hard mask layer. After the second dielectric layer is patterned, the vias defined in the silicon carbide hard mask layer are transferred into the first dielectric layer. Thereafter, the dual damascene structure is completed by filling the vias and interconnects with a conductive material.
In another integrated circuit fabrication process, the silicon carbide layer is used as an anti-reflective coating (ARC) for deep ultraviolet (DUV) lithography. For such an embodiment, a preferred process sequence includes forming a silicon carbide layer on a substrate. The silicon carbide layer has a refractive index (n) in a range of about 1.6 to about 2.2 and an absorption coefficient (K) in a range of about 0.1 to about 0.6 at wavelengths less than about 250 nm. The refractive index (n) and the absorption coefficient (K) are tunable, in that they can be varied in the desired range as a function of the composition of the gas mixture during SiC layer formation. After the silicon carbide layer is formed on the substrate, a layer of energy sensitive resist material is formed thereon. A pattern is defined in the energy sensitive resist at a wavelength less than about 250 nm (nanometers). Thereafter, the pattern defined in the energy sensitive resist material is transferred into the silicon carbide layer and, optionally, into the substrate.